Asterion

Charge. If Asterion moves at least 10 feet straight toward a target and then hits it with a gore attack on the same turn, the target takes an extra 9 (2d8) piercing damage. If the target is a creature, it must succeed on a DC 14 Strength saving throw or be pushed up to 10 feet away and knocked prone.

Labyrinthine Recall. Asterion can perfectly recall any path it has traveled.

Master of the Labrinth. Asterion can manipulate the Labyrinth's layout to its will.

Reckless. At the start of its turn, Asterion can gain advantage on all melee weapon attack rolls it makes during that turn, but attack rolls against it have advantage until the start of its next turn.

Daemon Prince. Unless its soul is trapped or destroyed, Asterion will reform the night after it dies.

Greataxe. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 17 (2d12 + 4) slashing damage.

Gore. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 13 (2d8 + 4) piercing damage, 2d10 acid damage.

Asterion may take 3 Legendary actions, recharging upon death.

Trapper.  One of three traps appears within the room, a Pit trap, a Dart trap or 2d10 Zombies.

Call. Asterion invokes the power of a higher being. This may be either Thanatos, or Asmodeus. This will last until death, and it may not invoke a different being until it dies.

Thanatos: Asterion deals 2d8 necrotic damage along side any melee attack, and gains +5 to it's constitution stat.

Asmodeus: Asterion gains a +10 to intelligence and wisdom, and can understand any language.

Raging Bull. Asterion may now make two actions in one turn. This effect lasts until it takes 50 or more damage.